This invention relates to a real-time digital data preprocessor for a refraction sounding system, and more particularly for a digital data smoother and significant values selector for the system.
Radio propagation characteristics in the atmosphere can be determined by refraction calculations from suitable atmospheric measurements similar to those made for conventional meteorological soundings which determine temperature, pressure, and humidity along a vertical profile. Typically, atmospheric measurement devices commutate and transmit these parameters to a remote receiver via telemetry where they are decommutated and recorded. These telemetry systems, however, lack the accuracy and resolution needed for the refraction calculations because of the noisy data telemetered. At least two different noise conditions occur. One occurs when a strong noise burst having a short time duration distorts only one of the measured telemetered data samples; another occurs when signal strength fades typically for a few seconds or less. During this fade-out the telemetry system's ambient noise level is large in comparison with the faded signal and causes loss of synchronization of the decommutator at the receiver resulting in distortions in measurements that persist beyond the noise duration. Frequent and prolonged losses of decommutator synchronization create gaps in the data large enough to mask information of interest. Systems presently used for calculating the atmosphere's refractivity versus altitude characteristics are therefore inadequate for determining the operating characteristics of radio-frequency propagation systems with the requisite accuracy and resolution.